Effects of subthalamic deep brain stimulation on dysarthrophonia in Parkinson's disease

Background: Motor deficits in Parkinson's disease (PD) are reduced by deep brain stimulation (DBS) of the subthalamic nucleus (STN), but the impact of this therapy on dysarthrophonic problems in PD remains controversial. We therefore aimed to disentangle the effects of STN DBS on the speech skills of long-term treated patients. Methods: Under continued medication, speech and motor functions of 19 patients with PD with bilateral STN DBS were studied when their therapeutic stimulation was active (STIM-ON) versus switched off (STIM-OFF). Per condition, perceptual speech ratings were given by: (i) the patients themselves, (ii) the treating physician, and (iii) professional speech therapists. Furthermore, single speech parameters were measured with a battery of technical exams in both STIM-ON and STIM-OFF. Results: STN DBS significantly worsened speech performance according to all perceptual rating methods applied. In contrast, technical measures showed DBS-induced improvements of single speech dimensions affected by the PD-specific motor disorder. These changes occurred independently of the reduction of motor impairment, which was consistently effectuated by STN DBS. Conclusion: In parallel to the beneficial effects on the motor symptoms of PD, STN DBS reduces designated disease-inherent dysarthrophonic symptoms, such as glottic tremor. However, these actions on speech are predominantly outweighed by the general dysarthrogenic effects of STN DBS, probably based on a decline of complex (eg, prosodic) functions. Thus, stimulation-induced speech impairment should be considered a likely problem in the course of this treatment.